Loading dock leveler assemblies normally embody a hingedly mounted loading ramp or deck which is adjustable between a stored position wherein an exposed surface thereof is substantially coplanar with the dock platform surface and an operative position allowing loading or unloading of the bed of a truck parked adjacent the front wall of the dock. An extension plate or lip is pivotally mounted on the front edge of the ramp and, when in an extended or cantilevered mode, bridges the gap which occurs between the rear end of the truck bed and the front wall of the loading dock.
It has been found, however, that certain safety problems may occur when such dock levelers are used. For example, dock personnel may inadvertently drive or push material handling equipment (e.g., a fork lift truck) off the front edge of the loading dock leveler when there is no vehicle parked adjacent the loading dock and the ramp is in the stored position.
To minimize the risk of such "accidental run offs" dock levelers have heretofore been developed that include various forms of barriers which physically obstruct and thereby prevent movement of material handling vehicles beyond the front edge of the dock leveler. For example, in certain dock levelers the pivot axis of the lip is set back a substantial distance from the rear edge of the lip so that the rear section of the lip between the pivotal axis and the lip rear edge projects above the ramp surface and forms a barrier when the lip is in a depending position with respect to the ramp. In such levelers, however, unless the ramp surface and the exposed surface of the lip are coplanar, when the lip is in an extended cantilevered position, the rear section of the lip still projects angularly upwardly to a varying degree above the loading ramp surface forming a vehicle barrier. This continued projection of the lip rear section may seriously obstruct the loading and unloading operations.
Recognizing this problem, several dock leveler assemblies have heretofore been developed with an automatic barrier which is either coplanar with or slightly below the exposed ramp surface when the lip is in an operative extended cantilevered position or in other positions. Examples of such dock leveler assemblies are disclosed in U.S. Pat. Nos. 4,920,598 and 5,040,258, wherein the ramp is pivotally mounted for movement between three positions--a stored first position in which the exposed ramp surface is substantially coplanar with the loading dock platform surface, an upwardly inclined second position, and a declining third position. The front edge portion of the ramp includes a pivotally mounted lip moveable between a stored vertical position and an operative outwardly extending cantilevered position. This lip integrally includes a barrier unit, a portion of which automatically projects above the ramp exposed surface to form a vehicle barrier of optimum height when the extension plate or lip is in the stored vertical position, and which, when the lip is in the outwardly extending cantilevered operative position, automatically retracts below the exposed ramp surface.
While in most circumstances it is desirable to employ an automatic material handling vehicle barrier when the dock leveler assembly is in a stored position, there are certain other circumstances when it may not be desirable to do so because the barrier may interfere with the end loading or unloading of a parked truck by a material handling vehicle. In such circumstances the material must be loaded onto or unloaded from the rear portion of the truck bed and the placement of the material would interfere with the lip if it was in a fully extended position.